'Bump" boiling can often happen in new, or very very smooth containers. An egg, for example. the bubbles of water vapor have nothing to form on, since the surface is so smooth. So the water will continue to heat without any visible signs of being beyond the boiling point. If the water is disturbed while in this state, it will boil all at once, quite violently. (If you bump it, hence 'bump' boiling, although there are other names) If you have some new glassware, specifically lab equipment, this can happen easily. Sometimes, lab workers will take some metal instrument and make a few scratches on the bottom of the vessel, making a place for vapor bubbles to form.
^
L what my science teacher told me